The present invention relates generally to circulating valves utilized in subterranean wellbores and, in a preferred embodiment thereof, more particularly provides a circulating valve which is responsive to the rate of fluid flow therethrough and associated methods of servicing a well.
Subterranean wellbores are generally filled with fluids which extend from the wellbore's lower terminus substantially to the earth's surface. For safety reasons, a column of fluid is usually present adjacent each fluid-bearing formation intersected by the wellbore, so that the column of fluid may exert a hydrostatic pressure on each fluid-bearing formation sufficient to prevent uncontrolled flow of fluid from the formation to the wellbore, which uncontrolled flow of fluid could result in a blowout. This is particularly so in an uncased wellbore.
In order to transport fluid, tools, instruments, etc. longitudinally within the wellbore, it is common practice to utilize a string of tubular conduit, such as drill pipe or production tubing, to which tools and instruments may be attached, and within which fluid may be flowed and tools and instruments may be conveyed. When such drill pipe, production tubing, etc. (hereinafter referred to as "tubing") is disposed within the wellbore, the fluid column is effectively divided into at least two portions--one of which is contained in an annulus defined by the annular area separating the outside surface of the tubing from the inside surface of the wellbore, and the other of which is contained within the inside surface of the tubing. Thus, fluid, tools, instruments, etc. may be transported within the wellbore attached to or within the tubing without disturbing the relationship between the fluid column in the annulus and the fluid-bearing formations intersected by the wellbore. An example of such operations may be found in the Early Evaluation System of Halliburton Energy Services, which is described in a U.S. patent application Ser. No. 08/578,489 entitled EARLY EVALUATION SYSTEM WITH PUMP AND METHOD OF SERVICING A WELL filed Dec. 26, 1995, the disclosure of which is hereby incorporated by reference.
Circulating valves are well known in the art. The primary purpose of a circulating valve is to selectively permit fluid flow from the fluid column within the tubing to the fluid column in the annulus. Where, for example, it is desired to pump a treatment fluid from the earth's surface to a particular portion of the wellbore, such treatment fluid may be introduced into the tubing at the earth's surface, pumped longitudinally through the tubing, and radially outwardly ejected from the tubing through a circulating valve into the annulus at the desired location in the wellbore.
In the lexicon of those familiar with subterranean wellbore equipment and operations, valves which permit flow from the interior of the tubing to the annulus are commonly known as circulating valves, primarily because the operation of flowing fluid from the interior of the tubing to the annulus is termed "circulating". Where, however, fluids are flowed from the annulus to the interior of the tubing (i.e., in a direction radially opposite to that described immediately above), the operation is termed "reverse circulating". Valves which permit reverse circulating are, therefore, commonly known as reverse circulating valves or simply "reversing valves", although they are sometimes considered a subset of circulating valves, in which case the term "circulating valve" is meant to encompass both types of valves. Hereinafter, the term "circulating valve" will be used to refer to a valve which selectively permits either radially inwardly directed or radially outwardly directed flow to and/or from the interior of the tubing.
Circulating valves may be further subdivided by the manner in which they are initially opened or closed, and whether or not, and in what manner, they may be reopened or reclosed. An example of a pressure operated, initially closed, and recloseable reverse circulating valve may be found in the MIRV (Multi-ID Reversing Valve) marketed by Schlumberger Well Services and described in U.S. Pat. No. 4,403,659 to Upchurch. A similar valve is the MCCV (Multi-Cycle Circulating Valve) also marketed by Schlumberger Well Services. Note that each of the MIRV and MCCV may permit, when opened, circulating as well as reverse circulating flow therethrough.
The MIRV is typically initially closed when run into the wellbore in the tubing string. It is opened by applying a set number and level of predetermined pressure pulses to the interior of the tubing at the earth's surface. The pressure pulses cause rotation of a continuous J-slot mechanism which selectively permits an inner tubular mandrel to axially displace within an outer tubular housing. When the mandrel is permitted to axially displace within the housing, the required number and level of pressure pulses having been applied to the interior of the tubing, a number of openings formed radially through the housing are uncovered, allowing fluid flow therethrough. At that point, continuous reverse circulation is permitted, and circulation is also permitted as long as the rate of circulating flow is sufficiently low.
The MIRV is reclosed by circulating flow through the openings at a rate sufficient to cause a predetermined pressure differential radially across the housing. The openings formed through the housing are relatively small in flow area for this purpose. When the predetermined pressure differential is achieved, the mandrel is axially displaced, compressing a spring, and the J-slot mechanism rotates to permit the mandrel to again cover the openings in the housing when the pressure differential is released. At this point, the valve is returned to its initial closed configuration and may again be opened by applying the required number and level of pressure pulses to the interior of the tubing.
The MCCV is operated similar to the MIRV, but includes a complicated array of circulating and reversing ports, and flow restrictors associated with each set of ports, such that changes in direction of flow (i.e., from circulating to reverse circulating, or from reverse circulating to circulating) may cause axial displacement of the mandrel to rotate the J-slot mechanism and, thereby, determine the axial disposition of the mandrel relative to the ports in the housing.
In addition to the complicated configuration and operation of the MCCV, there are several disadvantages of the MIRV and MCCV designs. Pressure differentials across the housing are created by flowing fluid through relatively small flow area openings and ports, thus limiting the flow rate through the openings and ports, with no provision for relatively unrestricted flow radially through the housing. This means that, for example, reverse circulating through the valves at a relatively high flow rate requires a large pressure to be applied to the annulus. Where the wellbore is uncased, such large pressure applied to the annulus is undesirable as it will tend to force wellbore fluid radially outward into permeable formations intersected by the wellbore, possibly causing damage to the formations and necessitating expensive remedial treatment.
Another disadvantage of the MIRV is that the restricted flow area openings are formed on the outer housing. Such small diameter openings are easily plugged by debris present in the annulus, and this situation is further exacerbated where the wellbore is uncased. By comparison, the fluid in the interior of the tubing is usually much cleaner than the fluid in the annulus.
Yet another disadvantage is that the J-slot mechanism of the MIRV and MCCV is unnecessarily complex, requiring multiple circumferential J-slot members, a dog formed on the inner surface of the housing, and multiple pins installed radially through the housing to engage the J-slots. The alignment and installation of the J-slot mechanism is tedious, and the number of parts provides increased opportunity for failure or jamming of one or more of them. The J-slot mechanism is expensive to manufacture. Furthermore, no provision is made for lubricating the J-slot mechanism or preventing debris from interfering with its operation.
A further disadvantage of the MIRV is that its biasing member, a spirally wound compression spring, is continually exposed to the fluid present in the annulus. As discussed above with regard to the restricted flow area openings on the housing, the fluid in the annulus tends to include a relatively large amount of debris. Since the spring is continually exposed to the annular fluid, such debris may accumulate about the spring and affect its spring rate and/or prevent its proper operation.
A still further disadvantage of the MIRV is that the pins installed radially through the outer housing also provide a limit to the axial travel of the mandrel. This use of pins as travel stops, which pins are also used to rotate multiple J-slots, invites damage to the pins, and, therefore, invites malfunction of the J-slot mechanism.
Another disadvantage of the MIRV is that it requires rotation of the J-slot mechanism within the outer housing while maintaining circumferential alignment of the mandrel with the outer housing. For this purpose, the mandrel is provided with an axially extending slot which engages a radially inwardly extending dog formed on the interior surface of the outer housing. A bearing is provided for rotational support of the J-slot mechanism on the mandrel. Such bearing, slot and dog add to the complexity of the MIRV, and further add to the expense of its manufacture and maintenance.
The MIRV requires a multiplicity of polished seal bores and outer diameters due to the fact that at least two differential pressure areas are required for its operation. One differential pressure area is required to shift the mandrel downwardly when the circulation openings on the housing are closed. The other differential pressure area is required to shift the mandrel downwardly when the openings are open. These polished seal bores, outer diameters, and associated seals, seal grooves, etc. further add to the manufacturing cost, maintenance cost, and complexity of the MIRV.
From the foregoing, it can be seen that it would be quite desirable to provide a circulating valve which does not have a complicated configuration and operation, which does not require flowing fluid through relatively small openings to produce pressure differentials across its outer housing, which does not have small openings formed through its outer housing for circulation of fluid therethrough, which does not require multiple J-slot members, multiple pins, or dogs formed on the inner surface of the housing, which does not require bearings or rotation of the J-slot mechanism relative to the mandrel, which does not require circumferential alignment of the mandrel relative to the outer housing, which does not require the pins to also serve as mandrel travel stops, which does not continually expose the J-slot mechanism and biasing member to annular fluid, and which does not require an inordinate number of polished seal bores, diameters, seals, etc., but which is easily and economically manufactured and maintained, which provides relatively unrestricted flow radially through the outer housing, which is specially adapted for use in uncased wellbores, and particularly for use in the Halliburton Energy Services Early Evaluation System, which is capable of reliable operation utilizing a single J-slot and pin, and which provides for lubricated and debris-free operation of the J-slot mechanism. It is accordingly an object of the present invention to provide such a circulating valve and associated methods of servicing a well.